JPS6042964B2 - image display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image display device suitable for displaying image information in, for example, a computed tomography device (hereinafter referred to as a "CT device").

When displaying an image containing a large amount of information (for example, an image such as an X-ray transmission image of a diagnostic area) as a visible image on a display using a CRT (cathode ray tube), etc., it is necessary to Tonal information is expressed by the shading (intensity modulation) of pixels (picture elements) in the image or by the color of the pixels, but the gradation density of the input signal is greater than the gradation display capability (clay scale) of the display device. If the price is high, the following conventional methods −
So, I was making that display.

B) [Method of matching the highest (gradation) value of the input signal to the maximum display intensity (gradation) of the display unit] In this case, the clay scale level of the display is coarser than the input signal density, so the input signal It has the disadvantage that the amount of information it has is reduced.

That is, minute differences in input signals cannot be determined. ])
[A method of displaying by enlarging a part of the gradation range of the input signal to fill the clay scale of the display] For example, on the display of a CT device, a predetermined CT number (for example -1000 ~+1000
Of the gradation information represented by the gradation information value of 2000 steps, the part within a certain CT number range (for example, C
Only the portion corresponding to the T number (range of 0 to 100) is displayed in gradation. In this case, although the amount of information contained in the input signal is not substantially reduced, the displayed image is a part of the input information, so it is necessary to display an image corresponding to each part. In other words, it has the disadvantage that you cannot see the whole thing at once. → [Method of logarithmically converting the input signal and displaying the converted value as the input signal of the display] In this case, the whole can be displayed, and at the same time, the whole information amount can be made uniform as shown in (a). Rather than subtracting it, the input signal is compressed and displayed in a form (logarithmic type) that matches the viewer's visual sense.

Of course, the amount of input information has decreased. In this way, conventionally, when displaying a gradation signal with high signal density on an image display with limited intensity resolution, it is necessary to reduce the signal density [(a) and (c)] or to change the signal Display was performed either by extracting and displaying only a part of the target range or by displaying [(mouth)], but either method was insufficient.

In addition, CT devices have many gradation steps for each pixel of a tomographic image, such as 200 tones in CT number, which makes them incomparable with conventional X-ray diagnostic devices. It is highly acclaimed as an excellent diagnostic device that can detect minute differences in tissue.

However, displays such as CRT display devices that display the tomographic images are generally only capable of displaying at most incremental gradations, so it is impossible to display all of the 2000 gradations mentioned above at once. It was possible. Figure 1 shows CT
This figure shows an example of the basic configuration of the apparatus, in which 1 is a radiation generating section that generates a radiation beam such as X-rays, 2 is a detection section for the radiation, and 3 is a radiation generating section 1 necessary for obtaining a tomographic image.
and a scanning mechanism unit that drives both or one of the detection units 2 to scan the radiation beam on the subject; 4 is a data collection unit that collects signals from the detection unit 2 during scanning;
5 calculates a tomographic image (image reconstruction) based on the data obtained from the data acquisition unit 4, and the relationship of each signal in the above equation is shown in FIG.

This calculation is performed according to the combination of two sets of comparison detection circuits for dividing the range of D into three as shown in the proviso, a combination of four arithmetic operation circuits that perform the calculation, and a combination of the outputs of the two sets of comparison detection circuits. It is clear that it can be constructed using a multiplexer circuit or the like for ultimately unifying the display density Pd. By the way, in an example of a conventional image display unit as shown in FIG. 2, for the value within the density window mentioned above,
Since the display density changes linearly, there is an arithmetic control section that controls the operation of the linear device; 6 is an image display section that displays the tomographic image obtained by the arithmetic control section 5; FIG. 2 shows in detail the image display unit 6 in the conventional device described above, and uses a method corresponding to the above-mentioned (mouth).

In the figure, 7 is an image memory that stores tomographic image information for one screen and can write/read data density Dd for each pixel, and 8 is a maximum value Pdmax and a minimum value Pd of display density.
9 is a window level adjuster for specifying the window level, that is, the median value WL of the one-tat density range (window) that you want to display; 10 is the window width, that is, ≠ one that you want to display. A window width adjuster 11 is used to specify the width Ww of the data density range, and a window width adjuster 11 performs predetermined arithmetic processing using the data density Dd, the maximum value Pdmax, the minimum value Pdmin of the display density, the window level WL, and the window width WW as input signals. An arithmetic circuit 12 for outputting the result display density Pd is an image display device which takes the display density Pd as an input signal and includes a synchronization signal adding circuit necessary for display and other general image signal processing circuits. Here, an example of a specific calculation formula in the arithmetic circuit 11 will be shown.

Named the window function, this linear window function can certainly recognize the entire range of the data density Dd as the display density Pd by changing it by combining WL and WW, but the contrast of the displayed image was monotonous, and it was not possible to enhance or attenuate the contrast in a certain data density range for observation.

The present invention was made based on the above-mentioned circumstances, and compresses a portion of an input image signal other than a desired region of interest, thereby reducing the amount of information contained in the input signal while minimizing the amount of information in the region of interest. It is an object of the present invention to provide an image display device capable of displaying the entire key range.

That is, the present invention is characterized in that in an image display device that modulates display gradation using image information consisting of gradation data for each pixel to obtain a visible display image, the gradation data of input image information is On the other hand, the present invention is configured to include modulation means for obtaining corresponding display gradation information with nonlinear characteristics that allow the position and range of the nonlinear portion to be set as desired.

Examples of the present invention will be described below. First, the principle of the first embodiment of the present invention will be explained.

The relationship between the amount of light exposure to X-ray film and film density is
As shown in FIG. 4, there is a logarithmic relationship (indicated by a linear region in FIG. 4) in the central density region, and the degree of gradation is determined by the type of film.

Also, if the amount of light exposure is extremely low or high,
The concentration approaches a constant value (at both ends of the horizontal axis in FIG. 4). This relationship can be approximated by where X is the light exposure amount and D(X) is the density.

Here, DO: Minimum density Dm; Center density [If the maximum density is Dmax, X1:
Light exposure amount value a corresponding to center density Dm; reciprocal of gradation (scale factor) Sgrl; symbolic function [i.e. S
grl(X1-X).

In the above relationship, if the light exposure amount is replaced with the input image signal and the film density is replaced with the display intensity of the display device, it can be applied to video display.

The advantages in this case are as follows. (1) By matching the minimum and maximum human power signals with the minimum and maximum display strengths of the display, the full range of the input signal is displayed.

(Ii) The input signal value that gives the center display strength (Dm) is
By selecting or adjusting 1, the region of interest can be arbitrarily selected.

This is because as long as the input signal value X1 is between the minimum input signal and the maximum human power signal Xmax, it can be arbitrarily selected regardless of these upper and lower limits, compared to the conventional linear display method. This allows for more flexible display. (I
By selecting or adjusting the O scale factor a, the gradation level of the displayed image can be arbitrarily selected.

It has a higher degree of freedom than the conventional logarithmic representation method. (Iv) By selecting the input signal value X1 to select the region of interest of the input signal, and further selecting the scale factor a and selecting the gradation, the vicinity of the region of interest can be precisely Not only is it possible to display the signal at a gradation level and center signal position that is optimal for diagnosis, but it is also possible to display the signal at the optimal gradation level and center signal position for diagnosis.

In particular, near the region of interest, the input signal and display intensity are approximately linear, resulting in an image that is easy to read for diagnosis.
(V) Since the characteristics are almost the same as those of X-ray film, direct
It is easy to compare with an X-ray film image obtained by radiography.

In this way, it becomes possible to effectively display input image signals that could not be obtained using conventional methods. FIG. 5 is a block diagram showing the configuration of this embodiment based on such a principle. In the same figure, the image input signal X is sent to the logarithmic amplifier 1C1
The signal is logarithmically converted and input to the inverting input terminal of the differential amplifier 1C2. A signal corresponding to 10g The output is This output is input to the multiplier 1C4 as it is on the one hand, and is inverted by the inverting amplifier 1C3 and input to the multiplier 1C4 on the other hand.
The product of these two inputs becomes the output of the multiplier 1C4.

This is further inputted to the antilogarithmic amplifier 1C, and its output is inputted to the differential amplifier 1C6 and subtracted from the reference voltage created by the variable resistor VR3 to obtain .

The output of this differential amplifier IC6 is input to a square root amplifier IC7, and its output is input to a multiplier IC8.

On the other hand, the output of the differential amplifier IC2 mentioned above is the output of the comparator I
It is also given to C9, where it is compared with zero potential, for example -0.6V if higher than zero potential) +0 if lower
．． 6V is output. That is, is output.

This is input to the non-inverting amplifier ICIO, where it is amplified to a value corresponding to the center luminance Dm of the display, and the multiplier IC
8 is input.

Therefore, the output of the multiplier IC8 is, and the output of the differential amplifier I
CII is further given from variable resistor VR4 (DO+
Dm) is added and output as.

This output signal D(X) is the CR
T is applied to the intensity modulation input of the display. Note that R1 to R8 in FIG. 5 are resistors, and Dl and D2 are constant voltage diodes.

In this way, the input image signal X is converted into the display intensity D(X) according to the above equation (2), and the above-described display is performed.

FIG. 6 shows a second embodiment of the present invention, and is shown as a detailed explanatory diagram of the image display invention in the CT apparatus shown in FIG.

In FIG. 6, the same parts as in FIG. 2 are given the same reference numerals, and detailed explanation of the invention will be omitted. 13 is a window constant adjuster for adjusting and setting a window constant, for example, an initial value; 14 is an amplitude A of a nonlinear window function, which will be described later.
An amplitude adjuster 15 is used to adjust and set F; 15 is the data density Dd, the maximum value Pdmax) and the minimum value Pdmi of the display density;
n) Window initial value WZ and window function amplitude A
Window variable W as intermediate output with F as input signal
An arithmetic circuit 16 which performs a predetermined calculation to be described later based on P and the corresponding window function value WF and finally outputs the display density PdN;
This is a window function generator that outputs a window function value WF corresponding to the window function value WF.

The input/output function of the window function generator 16 can be expressed mathematically as follows.

Here, the window variable WP is (Dd-WZ).

The window function f in equation (3) must be a monotonically increasing function in which the function value WF is uniquely determined for the variable WP in the range of . Next, a specific calculation formula in the arithmetic circuit 15 will be shown. In the above equation, K is a constant related to display density, which should be determined together when determining the window function f, and is a constant generated by the arithmetic circuit 15 itself or calculated from the value of Pbmax or Pdmin. .

Further, f-' is an inverse function of the window function f. 7th
The figure shows a specific example of the arithmetic circuit 15.
is a subtraction circuit for calculating (Dd-WZ) [=WP], and in addition to the subtraction result WP, it simultaneously outputs a sign signal indicating the sign of the subtraction result.

18 is a multiplication circuit that calculates AF-WF.

19 is a constant generation circuit that generates the display density constant K, 20 is an addition circuit that calculates (AF-WFfK), and 21 is (AF
-WFfB) and Pdmax and outputs a code signal.

22 uses the code signal given from the subtraction circuit 17 and the comparison circuit 21 as a control input, and outputs the signals Pdmax, Pdmin.
and (AF-WF+K) and outputs the selected one as the display density PdN,
The outputs of the subtraction circuit 17 and the comparison detection circuit 21 are set to logical values'
If '1' is positive and 'o' is negative or zero, when the sign output of the subtraction circuit 17 is '0', PdN is P
dmin is selected, and the sign output of the subtraction circuit 17 becomes ''1.
'', when the sign output of the comparison detection circuit 21 is ``0'', the output of the addition circuit 20 (AF-WF+
K) is selected and both sign outputs of the comparison detection circuit 21 are ``1'', Pdmax is selected as PdN.

With the configuration shown in FIG. 7, processing that satisfies equation (4) is performed.

8 to 11 show data density Dd and display density R when using the nonlinear window function according to this embodiment.
Some typical examples of elbow relationships are shown below.

That is, in FIG. 8, the following is used as a specific function of equation (3).

The above Exp is an exponential function. And the formula (4-2) is as follows.

In Figure 9, equation (3) is It is said that

The above 1n is a natural logarithm. And the formula (4-2) is
It is said that

In Figure 10, equation (3) is And the formula (4-2) is It is said that

Furthermore, in Figure 11, equation (3) is And the formula (4-2) is It is said that

In the above four representative examples, in FIG. 8, the contrast on the side where the data density is small, that is, the change in display density is made small, and the contrast is made large on the side where the data density is large.
In Fig. 9, the relationship is completely opposite to that in Fig. 8, and in Fig. 10, the contrast around the median value of display density is reduced.
Contrast is emphasized in various ways, such as by enlarging both ends and creating a relationship in FIG. 11 that is completely opposite to that in FIG. 10.

In particular, the window function shown in FIG. 11 is particularly effective because it can emphasize minute changes in data density and display a wider range of data density than conventional methods. The arithmetic circuit 15 in this embodiment is usually a digital circuit, which is more convenient for ensuring accuracy, but it may also be an analog circuit or a general-purpose information processing device such as a computer or a microcomputer. It is possible to obtain similar effects.

In addition, we have added a window function selection switch, configured the conventional linear window function and the above-mentioned nonlinear window function to be usable with a changeover switch, and made it possible for the operator to understand the window function curve. It may also be configured to include a window function curve display for display.

As described in detail above, according to the present invention, it is possible to effectively compress parts of input image information other than the desired region of interest, and to reduce the amount of information in the region of interest to a large extent. An image display device that can efficiently display the key range can be provided.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with various modifications without changing the gist thereof.

[Brief explanation of the drawing]

1 and 2 are configuration diagrams for explaining an example of region of interest display in a conventional CT apparatus, FIG. 3 is a characteristic curve diagram for explaining the display method of the same example, and FIG. 4 is a diagram of the present invention. 5th characteristic curve diagram for explaining the principle of the first embodiment of
The figure is a block diagram showing the structure of the first embodiment, FIGS. 6 and 7 are block diagrams showing the structure of the second embodiment of the present invention, and FIG.
Figures 1 to 11 are characteristic curve diagrams for explaining the operation of the second embodiment. ICl...logarithmic amplifier, IC2, IC6, ICll・
... Differential amplifier, IC3 ... Inverting amplifier, IC4, I
C8... Multiplier, IC5... Anti-logarithm amplifier, IC7
...Square root amplifier, IC9...Comparator, IClO・
...Non-inverting amplifier, ■R1-VR4...Variable resistor, D
l, D2...Diode, R1-R8...Resistor, 7
...Image memory, 8...Data generator, 12...
Image display device, 13... Window constant adjuster, 14
... Amplitude adjuster, 15... Arithmetic circuit, 16... Window function generator, 17... Subtraction circuit, 18...
Multiplier circuit, 19...constant generation circuit, 20...addition circuit, 21...comparison detection circuit, 22...selection circuit.

Claims (1)

[Claims] 1. In an image display device that modulates display gradation using image information consisting of gradation data for each pixel to obtain a visually displayed image, a nonlinear portion is 1. An image display device comprising modulation means for obtaining corresponding display gradation information with nonlinear characteristics whose position and range can be set as desired. 2. The image display device according to claim 1, wherein the modulating means can select and set the nonlinear function of the nonlinear portion of the nonlinear characteristic as desired.